Fuel nozzle and method of repair

ABSTRACT

A modular fuel nozzle tip for a gas turbine engine includes a body defining one or more fuel conveying passages extending therethrough, an annular cap having a radially inner shoulder surface interfacing with the peripheral end surface of the body to define a plurality of air channels extending through the head portion of the modular fuel nozzle tip. At least two fasteners fasten the annular cap to the body.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of U.S. patent application Ser.No. 12/574,841 filed Oct. 7, 2009, the entire contents of which isincorporated herein by reference.

TECHNICAL FIELD

The technical field generally relates to fuel nozzles, such as those foruse in gas turbine engines.

BACKGROUND

Gas turbine engine fuel nozzles can be both difficult and costly tomanufacture. Prior attempts to reduce manufacturing costs have resultedin fuel nozzles having two piece tips. By using a. two piece fuel nozzletip, the machining, drilling and finishing operations required tomanufacture such fuel nozzles are simplified. Difficulties arise,however, when processes such as brazing or sintering are used to fastenthe two nozzle pieces together. Under certain operating conditions, thebrazing or sintering may weaken and/or break and subsequent repair maybe difficult, costly or impractical. Hence, opportunities for costreduction and increased versatility of fuel nozzle tips do yet exist.

SUMMARY

There is provided a modular fuel nozzle tip for a gas turbine engine,the modular fuel nozzle tip comprising: a fuel conveying body definingone or more fuel conveying passages extending between an inlet end andan outlet end of the body, the outlet end having a head portion with aperipheral end surface, the head portion having web portions extendingradially therefrom, and at least two projections extending from the endof said web portions; an annular cap circumscribing only the outlet ofsaid fuel conveying body and having a radially inner shoulder surfaceinterfacing with the peripheral end surface of the fuel conveying body,the peripheral end surface and the shoulder surface defining a pluralityof air channels extending through the head portion of the modular fuelnozzle tip; and at least two fasteners fastening the annular cap to thefuel conveying body, said fasteners being circumferentially distributedabout the annular cap, each of said fasteners extending through theannular cap and into one of the projections.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures, in which:

FIG. 1 is a schematic axial cross-section view of a gas turbine engine;

FIG. 2 is an axial cross-section view of the present fuel nozzle tip;

FIG. 3 is an isometric rear view of the fuel nozzle tip of FIG. 2; and

FIG. 4 is a perspective cross-section view of the fuel nozzle tip ofFIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, amultistage compressor 14 for pressurizing the air, a combustor 16 inwhich the compressed air is mixed with fuel and ignited for generatingan annular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases. The fuel is supplied to thecombustor 16 via fuel nozzles whereby it is also mixed with thecompressed air flowing through the fuel nozzle tips. it will beunderstood however that the invention is equally applicable to othertypes of gas turbine engines such as a turbo-shaft, a turbo-prop, orauxiliary power units.

A modular fuel nozzle tip is generally shown at 20, as seen in generalon FIG. 1 and in detail on FIG. 2. The nozzle tip comprises two maincomponents, a body 22 and an annular cap 34, as best seen on FIG. 3. Theannular cap 34 is fastened to the body 22 with the use of fasteners 42,as seen on FIG. 2.

Referring now to FIGS. 2-4, the body 22 defines a central passagegenerally shown at 24 extending between an inlet end generally shown at26 and an outlet end generally shown at 28. The central passage 24 maybe adapted to receive a fuel delivery probe or a number of suitable fueldelivery conduits, connected to a fuel supply (not shown). The outletend 28 of the body 22 comprises a head portion 25 with a peripheral endsurface 30 surrounding a spray orifice, generally shown at 31, of thecentral passage 24. The head portion 25 comprises a plurality ofprojections 32, which will be explained in greater detail below.

The annular cap 34 circumscribes the spray orifice 31 of the body 22 andhas a shoulder surface 36 interfacing with the peripheral end surface 30of the head 25. The annular cap 34 further comprises an annular rim 38extending beyond the shoulder surface 36 and rearward towards the inletend 28 of the body 22, the annular rim 38 being concentric with, butradially spaced apart from, the body 22 and substantially parallel tothe central axis 44 of the central passage 24. The central axis 44 is alongitudinal central axis of the entire modular fuel nozzle tip. Theterm “substantially parallel” used herein is intended to encompass anorientation which is approximately, but not necessarily exactly,parallel to the central axis 44 of the central passage 24.

The peripheral end surface 30 of the head 25, and the shoulder surface36 of the cap 34 define a plurality of through air channels generallyshown at 40, at the interface between the cap 34 and the head 25, asbest seen on FIG. 3. The channels 40 extend substantially radially aboutthe spray orifice 31. The air channels 40 extend through the fuel nozzletip 20 and are defined by circumferentially distributed through slots 41extending across the peripheral end surface 30 of the head 25 and theshoulder surface 36 of the annular cap 34. The air channels 40, withtheir circumferentially spaced apart arrangement, result in web portions33 disposed circumferentially therebetween, the web portions extendingsubstantially radially from the head 25 of the body 22. The air channels40 are used to deliver air into the combustor 16 and also to interactwith fuel as it exits the spray orifice 31. The air channels 40 may beoriented to also comprise a tangential and/or axial component inrelation to the central passage 24 so as to promote atomisation of thefuel and/or induce a swirling motion of the air/fuel mixture as itenters the combustor 16. Accordingly, the term “substantially radially”used herein is intended to encompass orientations that have a radialcomponent but that may not necessarily be purely radial.

A plurality of projections 32 are integrally formed with the webportions 33 of the body 22 and extend axially towards the inlet end 26of the body 22, while being substantially parallel to the central axis44 of the fuel nozzle tip 20. These projections 32 may also be referredto as “fingers”. In a possible embodiment, the projections 32 have acircumferential width which is equal to the circumferential width of theweb portions 33.

The cap 34 and the body 22 are manufactured as separate parts and aresubsequently assembled and fastened together by at least two fasteners42 to form the fuel nozzle tip 20. In order to fasten the cap 34 to thebody 22, at least two diametrically opposed tight tolerance holes 46 aremade, using for example a drill although various other means may also beused to make the holes 46 in the annular rim 38 of the cap 34.Similarly, at least two diametrically opposed projections 32 of the head25 are chosen and one tight tolerance hole is made in each of theseprojections, which yields at least two diametrically opposed tighttolerance holes 48 in the projections 32.

Once the holes in the rim and the holes in the projections are formed,the shoulder surface 36 of the cap 34 is placed against the outlet endof the body 22 and in so doing, the shoulder surface 36 interfaces withthe peripheral end surface 30 of the head 25. Simultaneously, the holes46 in the annular rim 38 and the holes 48 in the projections 32 arecircumferentially aligned. This circumferential alignment forms aplurality of pairs of holes, each pair comprising one hole 46 in the rimand one hole 48 in a finger. A fastener 42 is then inserted in each pairof said holes 46 in the rim and said holes 48 in the projections. Thesefasteners provide an interconnection between the cap 34 and the body 22,which fastens the cap 34 to the body 22. In addition, the use offasteners provides a mechanical connection between the cap 34 and thebody 22, ensuring that the two pieces will not separate under engineoperating conditions.

In one possible embodiment, the cap 34 is first placed against the body22 and two diametrically opposed holes are subsequently made through theannular rim 38 and through two diametrically opposed projections of thebody 22, thus simultaneously forming the holes 46 in the rim 38 and theholes 48 in the projections 32. In another possible embodiment, the cap34 is first press fit onto the head 25 of the nozzle body 22, prior tothe forming of the holes. This is made possible because the peripheralend surface 30 has a frustro-conical configuration, which providesself-centering of the cap 34 and body 22.

To ensure minimal movement in the fasteners 42, the fasteners 42 mayadditionally be subsequently brazed into place. Because braze does notflow into tight fit joints, the braze will not flow between the body 22and the cap 34, but will only be present around the fasteners. Thefastener 42 may then be machined to be flush with the cap, so as to notprotrude outside of said cap.

In the particular embodiment described herein, the fasteners arecomprised of dowel type pins, although various other fasteners, pins ormeans of mechanical connection between the annular rim and theprojections may be used in place of a dowel type pin, such as forexample a key, a rivet or a threaded fastener.

An advantage of using projections to connect the cap to the body is thatthe projections help reduce thermal differential growth and also providesufficient flexibility to limit thermal stresses to an acceptable level,compared to previous methods of securing the cap to the body. Theseadvantages contribute towards a longer fatigue life for the fuel nozzletip 20.

Another advantage of the fuel nozzle tip 20 is repairability thereof.During the course of fuel nozzle operation, the annular cap 34 maybecome damaged, due to fretting or oxidation for example. The use of afastener as a connection element and the modular nature of the fuelnozzle tip 20 permit the cap 34 to be replaced or repaired independentlyfrom the body. To remove the cap 34, the fasteners 42 may be drilledout, or removed by other means, from the annular rim 38 and theprojections 32. Such other means can include machining operations, suchas milling, electro-discharge machining (EDM), or alternatively chemicalor electro-chemical material removal processes. The annular cap 34 maythen be removed from the body 22 and a replacement cap may be used inits place. The replacement annular cap may comprise the same, previouslyused, cap 34 which is repaired, or may comprise a new, previouslyunused, cap 34. New holes 46 may then be drilled through the annular rimof the replacement cap, if holes are not already provided in thisreplacement cap. During the repair of the fuel nozzle tip 20, it may benecessary to make new holes 48 in the projections 32 of the body 22. Insuch a case, new projections 32, which previously had been devoid ofholes, may be chosen, and holes 48 will subsequently be made in them. Aperson skilled in the art will recognize that this pertains to oneembodiment of this fuel nozzle tip, and that in another embodiment, itis possible to drill a new hole through an existing hole of a finger, ifsaid new hole is larger than said old one. The replacement cap may thenbe positioned against the body 22 and the holes 46 in the annular rim 38of the replacement cap may then be circumferentially aligned with theholes 48 in the projections 32 of the body 22. New fasteners 42 may thenbe used, such that each new fastener 42 is then inserted through one ofthe holes 46 of the rim 38 of the replacement cap and through a hole 48of one of the projections 32 of the body 22, thus fastening the new capto the previously-used body 22. The fasteners 42 may then be brazed aspreviously done in order to minimize any possible movement.

It should be noted that the fuel nozzle tip 20 should comprise at leasttwo holes 46 and at least two holes 48, so as to enable the use of atleast two fasteners 42, however more holes 46 in the rim and more holes48 in the projections may be formed if desired, thus enabling morefasteners 42 to fasten the cap 34 to the body 22.

Both the cap 34 and the body 22 may be manufactured using metalinjection molding (MIM) techniques out of the same or differentmaterials depending on the mechanical properties and high temperatureproperties that are desired for each part. The material for the cap 34may be selected so as to more efficiently withstand the harshenvironment inside the combustor 16 in comparison with the body 22. Inaddition to material costs, a person skilled in the art will recognizethat tooling costs may be reduced by producing the cap 34 and the body22 separately in comparison with a unitary nozzle. In the modular case,the body 22 does not have to be replaced as often as the cap 34. The useof a pin as a fastening means between the cap and the body permits amethod of repair, wherein only the manufacture of a new cap is needed inorder to repair the fuel nozzle tip 20, as opposed to replacing both thecap and the body. This enables repair costs to be reduced compared tothe traditional method of repair, wherein the whole fuel nozzle tip hadto be replaced. In addition, because the two parts of the fuel nozzletip are produced separately, simpler tooling may be used. For example,forming the slots 41 on the body 22 as opposed to through channels in aunitary nozzle significantly reduces the complexity of the mouldsrequired for MIM.

Although in this embodiment, the projections 32 of the body 22 and theannular rim 38 of the cap 34 extend axially towards the inlet end of thebody while being parallel to the central axis 44 of the central passage24, it should be noted that their particular direction may change,without departing from the scope of the invention disclosed. Forexample, the projections 32 and the annular rim 38 may extend at anangle relative to the central axis 44 of the central passage 24 of thebody 22, the angle ranging between 0 to 90 degrees, so long as they arein abutment with each other and permit the drilling of holes 46 in therim and holes 48 in the projections therethrough, for receiving afastener 42.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, it is apparent that the present modular nozzleconfiguration could be applied to simplex or duplex air-assistednozzles, to fuel nozzles mounted to internal fuel manifolds or havingstems, etc. Still other modifications which fall within the scope of thepresent invention will be apparent to those skilled in the art, in lightof a review of this disclosure, and such modifications are intended tofall within the appended claims.

1. A modular fuel nozzle tip for a gas turbine engine, the modular fuelnozzle tip comprising: a fuel conveying body defining one or more fuelconveying passages extending between an inlet end and an outlet end ofthe body, the outlet end having a head portion with a peripheral endsurface, the head portion having web portions extending radiallytherefrom, and at least two projections extending from the end of saidweb portions; an annular cap circumscribing only the outlet of said fuelconveying body and having a radially inner shoulder surface interfacingwith the peripheral end surface of the fuel conveying body, theperipheral end surface and the shoulder surface defining a plurality ofair channels extending through the head portion of the modular fuelnozzle tip; and at least two fasteners fastening the annular cap to thefuel conveying body, said fasteners being circumferentially distributedabout the annular cap, each of said fasteners extending through theannular cap and into one of the projections.
 2. The modular fuel nozzletip according to claim 1, wherein the at least two projections eachcontain a hole, the annular cap contains at least two holes and theholes of the projections and the holes of the annular cap arecircumferentially spaced and aligned.
 3. The modular fuel nozzle tipaccording to claim 2, wherein each fastener extends through both thehole of one of the projections and one of the holes of the cap.
 4. Themodular fuel nozzle tip according to claim 1, wherein a concentricannular rim extends from the shoulder surface of the annular cap, theannular rim being parallel to and abutted with the at least twoprojections of the body.
 5. The modular fuel nozzle tip according toclaim 4, wherein the fasteners extend through the annular rim of theannular cap, thereby fastening the annular rim to the projections of thebody.
 6. The modular fuel nozzle tip according to claim 5, wherein theprojections and the annular rim extend at an angle relative to a centrallongitudinal axis of the modular fuel nozzle tip, the angle rangingbetween 0 to 90 degrees.
 7. The modular fuel nozzle tip according toclaim 1, wherein the fasteners comprise at least two pins.